Method of and means for applying coatings



Patented July 10, 1945 ME'rnoD'oF AND MEANS Foa APPLYmG e coA'rmGs yFrank w. Hyman, New York, N. Y.

Application ctober 3, 1942, Serial No. 460,597

l (cl. 117-45) y] .9 claims.

The invention applies to a methodA of and neans for applying surfacecoatings to sheets of naterial and the general aim of the invention isio provide a novel means for and an improved nethod of applying uniformand evenly distribyited coatings to such rough surfaced materials isvarious types of rough pulp paper stocks.

An object of th'e invention is to provide a new and improved method ofand means for coating rough pulp paper stocks whereby to produce fromiuch stock flexible sheets having coatings there- :n selected to impartto the stock a desired proparty, characteristic, orcolor.

Another object is to provide a novel method-of :oating sheet materialwhich includes the step of applying to the surface to be coated,successive layers of coating material, each layer applied belng acontinuous single tone pattern whereby to insure uniform distribution ofthe material across th'e surface in an -accurately controlled quantity.

Another object is to provide a novel method in which each layer of thecoating is composed of substantially identical non-continuous particlesof material which in successive layers may have dissimilar shapes orcontours to insure overlapping of the particles of the successivelayers.

Another object is to provide a novel coating method of this character inwhich the successive layers applied to th'e surface to be coated, mayb'e of the same or dissimilar coating materials so that differentproperties or characteristics may be given to the stock.

A further object is to provide a novel method of coating rough surfacestocks by depositing on the rough surface discontinuous particles insuccessive layers, each layer of particles being deposited from anintagliated roll whereby the final Icoated sheet has a calendered finishand appearance.

Another object of the invention is to provide an improved means forapplying coating to a sheet of material which embodies a set of coatingmaterial applying rolls arranged to apply successively to a surfaceclosely spaced, discontinuous particles of coating material.

In conjunction with the foregoing, another Figs. 2, 4 and 6 each show ona greatly enlarged scale fragmentary surface areas of material applyingcylinders.

Figs. 3, 5, 7 and 8 show respectively on greatly enlarged scales thecoated stock as the successive steps of the method are performed'thereon.

While the invention 'is susceptible of various modifications andalternative constructions, I have shown in the drawing and will hereindescribe in detail', the preferred embodiment, but it is to beunderstood that I do not thereby in- -tend to limit the invention to thespecific form disclosed, but intend to cover all modifications andalternative constructions falling within the spirit and scope of theinvention as expressed in the appended claims.

. In discussing this invention, reference will be had to uniformity ofapplication of the coating material, to accuracy of control in theamount of coating fluid applied, to irregularities in the surl face tobe coated, and to the application of thin coatings. It should beunderstood that wherever these, or similar relative terms appear, theyare to be given substantially their extreme signiflcance.

This for the reason that th'e present invention aims at the applicationof coating materials with a high degree of precision and accuracy tosurfaces that may be rough and uneven as compared with' a smooth finishor calendered sur- Heretofore, the methods used in coating sheet lmaterials have been quite difficult to control as far as accuracy anduniformity in the amount of coating fluid applied is concerned. This isespecially true where sizable areas such as sheets or webs of paper areto be coated either completely or throughout a major portion of thearea. The application of coating by a spraying process is obviously notuniform. Where a. continuous coating is applied by such means as acoating-carrying roller, precise uniformity of the film of material onthe roller is diiiicult, if not impossible to obtain. A high degree ofaccuracy is moreover impossible because of the nature of the material tobe coated. A sheet or web of paper is not of uniform thickness when theuniformity is measured in ten-thousandths of an inch. Moreover, thefibrous structure of the paper itself, and particularly in such roughpulp paper stocks as Ynews print, kraft, tissue or the like, produces anuneven surface which. in terms of its microscopic appearance, isextremely irregular. Hence, even if the coating material, when appliedto such papers, is quite uniform, it will not remain so on the paper.While I have mentioned paper stocks particularly the invention may alsobe used ln coating cloth, woven fabrics and other materials so that theterm paper stock should beY considered as embracing such othermaterials.

A further disadvantage of present coating methods is in the fact thatvery thin coatingscf material cannot be applied. The relatively thickcoatings applied by rolls cannot dry substantially instantaneously and arelatively long drying period must elapse or the coated sheet must bespecially treated before it can be handled again.

In view of these factors, it has heretofore been dimcult, and in someinstances impossible, 'to produce coated papers or the like which areeconomically and commercially acceptable for such uses as wrappingpapers for cigarettes and tobacco, food, meat products, for insulation,and in general for any use requiring a sheet having predeterminedproperties and characteristics.

I have discovered that the dimculties mentioned above can be eliminatedby a method according to the present invention which includes the stepor steps of applying to the surface to be coated, successive layers ofcoating material, each of which layers is composed of regularly andclosely spaced minute applications of a selected coating material, theminute applications being of a character which will produce a continuoussingle-tone pattern. Thus the applied material may be in the form ofclosely spaced thin lines or closely spaced discontinuous minuteparticles. The close spacing of the particles is so vdetermined that,although-individually deposited on the sheet, they may run or "bleed"together. 'I'he exact spacing and the size of the individual particlesor width of the lines is dependent upon the material to be deposited andthe quantity of material desired in a particular layer.Characteristically, however, they are so small (on the order of .01 inchor less) that they have no appearance of individuality to the naked eye.Application by way of particles is preferred. However, use of this termherein is to be considered as embracing also material application in theform of spaced lines.

Preferably the layers are applied by means of sets of what may be termedsingle-tone intagliated cylinders or rolls, and while satisfactoryresults may be obtained by using a set of rolls (the number of rolls isdetermined by the number of layers to be applied) each having the sameform oi' intagliations therein, I find that substantially improvedresults are secured where the intagliations differ in form or shape onsuccessive rolls. In either event, the particles of each layer, beingclosely and evenly spaced, will run or bleed together to produce a layerwhich is of substantially uniform thickness. The quantity of materialper unit area in each layer is controllable with extreme accuracy byproperly dimensioning the intagliations. The particles of materialdeposited in any layer will overlap the margins of the materialdeposited in a preceding layer, whether the intagliatlons are similar ordissimilar, as a result of which any minute irregularities in any one-layer will be compensated for by the overlap of the particles of asucceeding layer.

In practicing the present process, the minute Vsize oi the depositedparticles insures that the layers will be relatively thin, usually onthe order of a few thousandths of an inch, and each layer will thereforedry rapidly. Accordingly the process is well adapted for coatingcontinuous webs of area on the intagliated cylinders.

material. Moreover, different coating materials may be easily applied insuccessive layers to introduce ertain desired properties,characteristics or color o the coated sheet.

It is possible by my process, to apply any coating material that may bedeposited by such means as an intagliated cylinder. For example, suchmaterials as asphaltum, aniline dyes, clay bodies, lacquer,formaldehyde, resinous coatings, various types of inks, caseinsolutions, various forms of glues, latex base solutions, metallic andnonmetallic powders in liquid form (for example lead,

copper, aluminum, synthetic resins, and carbon) l and synthetic andnon-synthetic waxes may be applied by my process. It will, of course, beunderstood that the size of the intagliations in any roll will depend onthe type of coating material to be applied, its viscosity, the amountofpigment, if any, therein, and the coating deposit required. Theviscosity of the coating fluid may vary anywhere from the fluidity of'water up to a 65 per cent powder solid in solution.

The drawings herein (with the exception of Fig. 1) showdiagrammatically, and in a scale greatly exaggerated, the steps of theprocess and representative shapes of the intagliated cylinders which Imay employ in practicing the process. Fig. l shows diagrammaticallyapparatus for practicing the method in the application of a successionof coating layers to both sides of ay web of paper. In this figure thenumeral 20 designates a roll of paper to be treated. Instead of thisarrangement, however, the paper may be taken directly from the papermaking machine. A series of intagliated rolls designated 2l, 22, 23 and2| are each arranged for cooperation with an impression roll 25 to actsuccessively on the web of paper 28 which runs over guide rolls 21 andpasses between the intagliated and impression rolls. Suitable coatingmaterial for each intagliated roll is supplied by a trough or reservoir28 in which the roll runs partially immersed, a conventional doctorblade 29, or the like, being provided to remove excess fluid. A secondseries of intagliated rolls and associated elements indicated generallyat lli, apply coating material to the reverse side of the web. Shouldthe character of the material applied by any roll require it, a simpleheatinil or drying means, 3|, such as a heating roll or pipes or an airdryer, may be located for heating the web after it leaves an intagliatedroll.

As has been mentioned, any complete coating will be composed ofsuccessively applied layers of discontinuous particles. The quantity ofmaterial applied-per unit area depends on the number and size of theparticles in that area which in turn depends on the number and size ofthe material-carrying cells or depressions in the same To produce acoating having any desired characteristic, property, color ofcombination thereof, a set of intagliated cylinders will be used whichare so correlated that each will apply a required layer of particles ina predetermined overlapping relation to the particles in a precedinglayer or to the inter-particle spaces thereof.

The intagliated rolls or cylinders employed in my coating method, may beproduced in several ways. Thus, I may employ cylinders on which thedesired intagliations have been produced by photochemical reproductionin which a sensitized carbon tissue which has been exposed to a suitablecontinuous toned screen is applied to the cylinder and the cylinder thenetched. This process is not preferred since it is impossible toeliminate the iated cylinders is by the use of knurling tools in theform of cylindrical members of suitable dimensions having lon their'cylindrical surfaces cutting dies or projections arranged to cut,impress or form complemental cells or depressions in the surface of thecylinder. In forming a cylinder a knurling tool having cutting dies ofpredetermined form thereon is caused to pass over the surface of thecylinder, thereby forming a continuous single tone pattern ofintagliations therein. A wide variety of shapes of the cutting dies orprojections on the knurling tool may be employed. For example, the formof the depressions may be squares, rectangles, circles, crescents, crthey may be in the form of letters such as the letters V, U or S." Ashas been mentioned, the size, shape and depth of the depressions in theintagliated cylinder are determined by the character and quantity of thematerial to be applied by that cylinder and the selected shape orcontour of the depression on any cylinder will, to a considerableextent, be determined by the shape of the depressions on the cylinderfor applying a preceding or succeeding layer. Hence the severalintagliated cylinders forming a, complete set for applying a givendeposit a layer of particles over the first applied laye 34. This secondlayer is 'indicated at 36 in of the particles and their bleedingtogether have smoothed out the minute irregularities of the layer 34firstapplied. The cylinder shown in Fig. 6 has substantially rectangulardepressions 31 producing, as shown in Fig. 7, the third layer 33 whichis more even and uniform than either of the preceding layers. If therectangular depressions are Joined at their ends a spaced line formationwill be obtained which is discontinuous across one dimension of thesheet. A fourth layer 39 may be applied as shown in Fig. 8 by anintagliated cylinder similar to that shown in Fig. 2. By way of example,the depth of cells or depressions of these various cylinders may be onthe order of .002 inch for the square and crescent-shaped intagliatonsof Figs. 2 and 4, and .001 inch for the rectangular intagliations ofFig. 6. i

It will be evident from a. consideration of these several forms ofintagliations that the margins of the successively applied layers ofparticles will overlap to insure complete coverage of the stock and thatthe particles in each layer will run or bleed together to form auniform, even layer.

. This is particularly true of the second and succoating have apredetermined correlation to afford the best overlapping of theparticles of the successive layers.` y

The knurling tools have their cutting dies or projections formed withmicroscopic precision by an engraving process or the like. For example,a, knurling tool may have cutting dies or projections shaped to producea square intagliation with a 150 line spacing, which on the basis of atwo and one-half screen ratio, would produce a depression or cell .0047inch square with a spacing between cells of approximately .002 inch anda cell depth of from .0062 inch to .008 inch. Preferably the cells taperinwardly slightly. After the depressions are formed the intagliatedcylinder is ground or otherwise polished, and thereafter chrome platedor finished to prevent wear.

I may mention that while I prefer to employ intagliated cylindersprepared by the use of knurling tools because of the greater precisionFig. '2 has square cells or depressions .32 and the form of the layerapplied thereby to the stock 33 is indicated roughly at 3l in Fig. 3.This layer being the one iirst applied may, as shown, be somewhatirregular because the penetration of the fluid into the stock and theirregularities of the rough stock may prevent the particles frombleeding evenly together. Fig. 4 shows crescent- Ashaped intagliations35 which are aranged to ceeding layers and for this reason the layerfirst applied will, in most instances, be a prime coat capable ofpenetrating the stock and adapted to provide a strengthening foundationfor the other layers by firmly binding the stock fibers together.

An important and unexpected feature of the invention results from theaction cn the paper stock of the surface portions 40 of the intagliatedcylinders which separate the cells or depressions therein.l It appearsthat when a rough nber paper stock, such as news print, is treated,these surface portions 40 of the cylinder will depress the areas of thefibers engaged thereby while depositing coating material on theintervening fibers. The applied pressure tends to iron or smooth out thefibers and in effect calenders the stock throughout the compressed areasWhile the bleeding of the applied coating material tends to bind thefibers in that condition. During the application of the successivelayers the remaining areas will likewise be pressed down with the resultthat at the end of the coating operation the coated surface of the stockhas the smooth finished appearance of a calendered sheet.

The following example is given as an illustra tion of the method ofcoating a thirty-pound news -print stock where it is desired to increaseits weight to forty-two-pound stock, color it and make it moistureproof.'I'he first layer would be a stock penetrating priming material havingmoisture proof properties deposited in a quantity which adds six poundsto the weight of the stock. The next layer would be a tinted orpigmented material deposited in a quantity to add four pounds to thestock weight. The nal coating would be a moisture proof materialincreasing the weight of the stock by two pounds. Thus the total weightof the coated stock would be forty-two pounds and the stock would betinted and moisture proof.

Such a coating will be accurate and uniform in thickness. The coatedmaterial will be flexible and the coating thereon will be highlyresistant to breaking or cracking due probably to the laminated effectafforded by the successive layers of coating. vThe invention. of course.may

g. 5 which indicates how the overlappingv f bution over its surface andwith the intagliations in each roll arranged to overlap only partiallythe area of registry on the web for a corresponding intagliation in thepreceding roll, flowing liquid coating material onto each of saidintagliated rolls, and doctoring away the excess material from each rollto leave deposits of substantially uniform volume in the intagliationsfor transfer from the latter to the web as such web .is pressed inrolling contact with the rolls.

2. A continuous coating method for webs. which comprises, passing theweb continuously through a 'plurality of successive roll couples inwhich the web is led in each couple between the bite of a pair of rollsconsisting of an intagliated roll and a coacting impression roll, theintagliations in the intagliated roll of each couple all being of thesame size and shape as every other intagliation in that same roll andlocated thereon in a pattern of uniform distribution bothcircumferentially and longitudinally of the roll, but with theintagliations in the intagliated rolls of each couple or couplesfollowing the first couple overlapping although slightly out of registrywith the portion of the web presented to the corresponding intagliationson the intagliated roll in the preceding couple. flowing liquid coatedmaterial onto each of said intagliated rolls. and doctoring away theexcess material from each intagliated roll to leave in the intagliationsin the latter deposits of accurately determined volumei for applicationto the web as it passes over the same.

3. The method of coating a web which comprises fiowing liquid coatingmaterial on a roll in a first roll couple in which such roll hasintagliations of uniform size and shape distributed in a pattern thereonwhich is uniform both circumferentially and longitudinally of the roll;doctoring away the excess coating material from the intagliated roll toleave substantially equal deposits of coating material in theintagliations; transferring to one side of the web, by rolling pressureapplied to the web in passing the same through said couple, the depositsfrom said intagliations in a pattern of minute mounds matching thepattern oi' the intagliations and with each r mound constituted bymaterial from a corresponding intagliation; and depositing furthermaterial on the same side of the web by repeating the same steps in asecond roll couple also having a cylinder bearing minute intagliationsof uniform size and shape and which are. as in the first. distributed ina pattern thereon which is uniform both circumferentially andlongitudinally of the cylinder but in which the individual intagliationsare slightly out of registry with the mounds deposited on the web in thefirst couple.

4. 'I'he method of coating a web which comprises flowing liquid coatingmaterial on a roll in a first roll couple in which such roll hasintagliations of uniform size and shape distributed thereover in apattern of overall coverage which is uniform both circumferentially andlongitudiasados? nally of the roll; doctoring away the excess materialfrom the intagliated roll to leave substantially equal deposits ofcoating material in the intagliations; transferring to one side of theweb, by rolling pressure applied to the web in passing the same throughthe couple. deposits from said intagliations in a pattern of minutemounds; and depositing further material on the same side of the web byrepeating the same steps in a second roll couple also having a cylinderbearing an overall pattern of uniformly distributed minute intagliationsof uniform size and shape but each of' which is of a different shapethan those on the intagliated roll in the first couple.

5. The method of coating a web which comprises passing the samecontinuously through a succession of pairs of intagliated and impressionrolls with the intagliated roll in each pair bearing a uniformlydistributed overall pattern of intagliations, each intagliation in eachintagliated roll being oi' the same size and shape as every otherintagliation in that same roll but of a different shape than those inevery other intagliated roll in the series. flowing liquid coatingmaterial onto each of the intagliated rolls. and doctoring away theexcess coating material from each intagliated roll.

6. The method of coating a web which comprises passing the samecontinuously through a succession of pairs of intagliated and impressionrolls with the intagliated roll in each pair bearing a uniformlydistributed overall pattern of intagliations, each intagliation in eachintagliated roll being of the same size and shape as every otherintagliation in that same roll but of a different size than those inevery other intagliated roll in the series, flowing liquid coatingmaterial onto each oi' the intagliated rolls, and doctoring away theexcess coating material from each intagliated roll.

7. An apparatus for coating a web comprising, in combination, aplurality of roll couples each including an intagliated roll and acoacting impression roll, means for supplying liquid coating material torespective ones of said intagliated rolls and for doctoring away theexcess thereon to leave deposits of coating material in theintagliations in such rolls, means for guiding a traveling web throughsuccessive ones of said couples with a plurality of said intagliatedrolls contacting the same face oi' the web, and each of said intagliatedrolls having the intasliations therein distributed thereover in anoverall pattern which is uniform both circumferentially andlongitudinally thereof and in which each intagliation in each roll is ofthe same size and shape as every other intagliation in that same rollbut located to be slightly out of registry with the portion of the webface contacted by any intagliation on any other roll in the series whichcontacts the same face of the web.

8. An apparatus for coating a web comprising, in combination, aplurality of roll couples each including an intagliated roll and acoacting impression rolll means for supplying liquid coating material torespective ones of said intagliated rolls and for doctoring away theexcess thereon toleave deposits of coating material in the intagliationsin such rolls, means for guiding a traveling web through successive onesof said couples with a plurality of said intagliated rolls contactingthe same face of the web, and each of said intagliated rolls having theintagliatlons therein distributed thereover in an overall pattern whichis uniform both circumferentially and longitudinally thereof and inwhich each intagliation in each roll is of the same size and shape asevery other intagliation in that same roll but of a different shape thanthe intagliations in every other one of the intagliated rolls contactingthe same face of the web.

9. An apparatus for coating a web comprising, in combination, a.plurality of roll couples each including an intagliated roll and acoacting impression roll, means for supplying liquid coating material torespective ones of said intagliated rolls and for doctoring away theexcess thereon to leave deposits of coating material in theintagliations in such rolls, means for guiding a traveling web throughsuccessive ones o1' said couples with a plurality `of said intagliatedrolls contacting the same face of the web, and each of said intagliatedrolls having the intagliations therein distributed thereover in anoverall pattern which is uniform both circumferentially andlongitudinally thereof and in which each intagliation in each roll is ofthe same size and shape as every other intagliation in that same rollbut of a different size than the intagliations in every other one of theintagliated rolls contacting the same face of the web.

' FRANK W. HYMAN.

